1. Field of the Invention
The present invention relates to an improved conduit spacer system and, more particularly, to base and intermediate units for supporting a plurality of conduits and for maintaining horizontal and vertical separation between such conduits.
2. Description of the Prior Art
In a conventional underground installation of electrical cables, the cables are run through conduits placed in a ditch and imbedded in concrete. These conduits generally are less than six inches in diameter. Utility company specifications and municipal code requirements often set forth a minimum spacing between adjacent conduits in a ditch and between each conduit and the bottom and sides of the ditch. Typical minimum spacings range from one and one-half inches to three inches. Therefore, one cannot simply place the conduits in a ditch without some means for maintaining the required separation therebetween.
In the past, base plates or spacers have been used to support electrical conduits above the floor of a ditch and/or to maintain separation between adjacent conduits. A problem encountered with base plate-type supports is that as concrete is being poured into the ditch to imbed the conduits, the force of the concrete tends to shift the position of the conduits on the base plates. Thus, to ensure that the minimum required separation will be maintained while pouring the concrete, it is often necessary to tie the conduits to the base plates. Such a tying operation is time-consuming and hence adds considerably to the cost of an underground conduit installation.
Another approach of the prior art has been to provide coupling collars at the joints between adjacent conduit sections. These coupling collars are generally square in shape, typically having a cradle at the top for receiving another conduit. Such coupling collars have significant disadvantages. For example, they can be used only at the intersection of adjacent conduit sections, thus significantly limiting their placement within a ditch. Moreover, each conduit must be placed carefully in the ditch atop the cradle of the subsequent conduit and such operation is time-consuming and adds considerably to the cost of an underground conduit installation.
In my U.S. Pat. No. 3,643,005, there is disclosed a unitary spacer for maintaining separation between electrical conduits in a ditch. Such spacer comprises a short tubular section having an inner diameter slightly larger than the outer diameter of the conduit with which the spacer is employed and an annular disc-shaped portion which extends radially outwardly from the tubular section and is provided at the periphery with a flanged rim. The rim supports the spacer-conduit assembly while the tubular section maintains the spacer perpendicular to the conduit at all times. Such a spacer readily may be slid over a conduit and positioned anywhere along the length thereof. Since the spacer is circular, minimum spacing is ensured between adjacent conduits or between the conduits and the wall or floor of the ditch, even though the conduit is not carefully placed in the ditch or shifts in position during pouring of the concrete.
While the spacer of my prior patent is a significant improvement over spacers used heretofore, users thereof often have two objections thereto. The first is that it is not convenient to stack conduits one above the other using such a unitary spacer. Secondly, the spacer must be slid over a conduit from the end thereof and this is often inconvenient when installing long conduits.
In my U.S. Pat. No. 4,183,484, there is disclosed a conduit spacer rack comprising a plurality of units which may be interconnected to form a rack for supporting a plurality of conduits in parallel, spaced-apart relationship. Each of the units comprises four generally coplanar arms emanating from a central hub in mutually orthogonal directions, first and second adjacent arms having a predetermined width and thickness, third and fourth adjacent arms forming channels at the free ends thereof, the width and depth of the channels formed in the third and fourth arms being approximately the same as the width and thickness of the first and second arms whereby the third and fourth arms are adapted to receive the first or second arms of adjacent units. Such units may be readily assembled into a rack to stack any number of conduits, one above another.
While the modular conduit spacer rack of my later prior patent is also a significant improvement over spacers used heretofore, one problem prevalent with virtually all prior art spacers, including the spacers of my prior patents, is that the spacers must be assembled for use with conduits. The assembly procedure is time-consuming and, with the escalating cost of labor, results in a significant labor element in the total cost of an underground conduit installation. Accordingly, the industry is presently searching for a spacer system which can be assembled very rapidly and conveniently to minimize the cost of an underground conduit installation.
In my copending patent application Ser. No. 045,303, filed June 4, 1979, and entitled Conduit Spacer System, there is disclosed a system for supporting a plurality of conduits above another in parallel, spaced-apart relationship including a base unit for supporting the bottom conduit, the base unit comprising a base and a U-shaped member having an open end for receiving the bottom conduit and supporting same, and an intermediate unit including first and second U-shaped members, the open ends of which extend in opposite directions whereby an intermediate unit can be pushed down onto one conduit and positioned to support another conduit thereabove. By continuing this process, multiple conduits can be supported and spaced one above another. Each unit includes matching interlocking means attached to opposite sides thereof whereby adjacent units may be interconnected to support multiple columns of conduits with a desired horizontal spacing.
While the conduit spacer system of my copending application represents a significant improvement over spacers used heretofore, users thereof often have several objections thereto. The first is that when lowering a conduit into a ditch onto a series of intermediate units, too much time is often taken in locating the conduits correctly. Secondly, while it is relatively easy to push a conduit into an intermediate unit or a base unit to be supported thereby, it is similarly easy to remove the conduits therefrom and this often occurs when concrete is poured into a ditch and the conduits float upwardly. Thirdly, it is not convenient to stack different sizes of conduits one above the other, or to vary the horizontal spacing between adjacent columns of conduits.